terraform: Interpolate if there are any interpolations [GH-159]

CHANGELOG.md

@@ -35,6 +35,7 @@ BUG FIXES:
   * core: The `file()` function can load files in sub-directories. [GH-213]
   * core: Fix issue where some JSON structures didn't map properly into
      Terraform structures. [GH-177]
+  * core: Resources with only `file()` calls will interpolate. [GH-159]
   * providers/aws: Fix issues around failing to read EIPs. [GH-122]
   * providers/aws: Autoscaling groups now register and export load
     balancers. [GH-207]

config/raw_config.go

@@ -25,6 +25,7 @@ const UnknownVariableValue = "74D93920-ED26-11E3-AC10-0800200C9A66"
 // information from deep within the structure.
 type RawConfig struct {
 	Raw       map[string]interface{}
+	Interpolations []Interpolation
 	Variables map[string]InterpolatedVariable
 
 	config      map[string]interface{}
@@ -87,9 +88,12 @@ func (r *RawConfig) Interpolate(vs map[string]string) error {
 
 func (r *RawConfig) init() error {
 	r.config = r.Raw
+	r.Interpolations = nil
 	r.Variables = nil
 
 	fn := func(i Interpolation) (string, error) {
+		r.Interpolations = append(r.Interpolations, i)
+
 		for k, v := range i.Variables() {
 			if r.Variables == nil {
 				r.Variables = make(map[string]InterpolatedVariable)

config/raw_config_test.go

@@ -9,6 +9,7 @@ import (
 func TestNewRawConfig(t *testing.T) {
 	raw := map[string]interface{}{
 		"foo": "${var.bar}",
+		"bar": `${file("boom.txt")}`,
 	}
 
 	rc, err := NewRawConfig(raw)
@@ -16,6 +17,9 @@ func TestNewRawConfig(t *testing.T) {
 		t.Fatalf("err: %s", err)
 	}
 
+	if len(rc.Interpolations) != 2 {
+		t.Fatalf("bad: %#v", rc.Interpolations)
+	}
 	if len(rc.Variables) != 1 {
 		t.Fatalf("bad: %#v", rc.Variables)
 	}

terraform/context.go

@@ -305,11 +305,6 @@ func (c *Context) computeVars(raw *config.RawConfig) error {
 		return nil
 	}
 
-	// If there are on variables, then we're done
-	if len(raw.Variables) == 0 {
-		return nil
-	}
-
 	// Start building up the variables. First, defaults
 	vs := make(map[string]string)
 	for k, v := range c.defaultVars {